CN1090847C - Method and device for improving receiver immunity - Google Patents

Abstract

The method and apparatus of the present invention improves the immunity of the radio receiver. The invention relates to a device for improving the radio frequency interference immunity of a radio receiver, which comprises: a first switch coupled to the received signal, the switch having a first position and a second position, the second position coupled to the bypass path; a first amplifier for amplifying the received signal, the input terminal of the first amplifier being coupled to the first position of the first switch, and the output terminal of the first amplifier being coupled to the bypass path; a controller coupled to the first switch transitions the switch to a closed position in response to the received signal exceeding a predetermined power level. A method of improving radio frequency interference immunity of a radio receiver is also provided.

Description

Method and device for improving receiver immunity

technical field

The present invention relates to wireless communications. In particular, the present invention relates to improvements in the immunity of wireless communication receivers.

Background technique

There are a variety of cellular radiotelephone systems in use today. These systems include the "Advanced Mobile Phone System" (AMPS) and two digital cellular communication systems: Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA). The implementation of a digital cellular communication system solved the capacity problems encountered by AMPS.

All cellular radiotelephone systems work by multiplying antennas to cover a geographic area. The antenna radiates into an area known in the art as a cell. AMPS cells are independent and thus different from CDMA cells. This makes it possible for the cell antennas of one system to be located within the cells of another system. Also, in certain systems (AMPS, CDMA and TDMA), there are two service providers within a given area. These service providers often choose to place cells in geographically different locations than their competitors, so that a situation exists where a radiotelephone for system 'A' may be far from the closest cell for that system and far from the nearest cell for system 'B'. 'The cellular area is near. This situation means that the signal to be received becomes weak due to strong multitone interference.

Such scrambling of system antennas can cause problems for mobile radiotelephones registered in one system (eg, a CDMA system) and traveling close to another system's antenna (eg, an AMPS antenna). In this case, the AMPS signal may interfere with the CDMA signal being received by the radiotelephone due to the proximity of the radiotelephone to the AMPS cell or the higher power of the AMPS forward link signal.

Distortion components are produced by the multi-frequency acoustic interference of AMPS signals encountered by radiotelephones. If these components fall within the CDMA frequency band used by the radiotelephone, they can degrade receiver and demodulator performance.

In AMPS systems, often the carrier (A and B bands) inadvertently interferes with a competitor's system. The aim of cellular mobile communications companies is to provide high signal-to-noise ratios to all users of their systems by locating cells close to the communication site or close to the users, and radiating FCC-limited power to each AMPS channel. Unfortunately, this technique provides better signal quality for the carrier's system at the expense of interfering with the competitor's system.

Intermodulation distortion caused by situations such as those described above is defined by the peak spurious level produced by two or more single-tone signals injected into the receiver. Most often, receivers use the third-order input acquisition point, or IIP3, to define the third-order distortion level. IIP3 is defined as the input power (in the form of two tones) required to produce a third order distortion product equal to the power of the input two tones. As shown in Figure 13, IIP3 can only be inferred linearly when nonlinear components such as amplifiers are below saturation.

As shown in Fig. 14, when two single-tone signals are injected into the receiver, three-segment distortion components are generated. Tone signal #1 is at frequency f1 with a power level of P1 (dBm). Tone signal #2 is at frequency f2 with a power level of p2 (dBm). Typically, P2 is set equal to P1. Third-order distortion components are generated at frequencies 2xf1-f2 and 2xf2-f1 at power levels P12 and P21, respectively. If P2 is set equal to P1, the spurious components should be equal, or P12 and P21 should be equal. The signal fc is injected at a power level Pc, indicating that in this case the added distortion is equal to a low level signal. If there is a filter that filters out f1, f2, and f21 after generating the distortion, the power at f12 will still interfere with the signal power at fc. In the example of Fig. 14, for CDMA application, the goal is that the intermode power P12 should be equal to the signal power -105dBm of the total power of two tone signals being -43dBm, so IIP3 must be > -9dBm.

Known in the art, the IIP3 of a nonlinear component is defined as follows:

IIP3=IM3/2=Pin(dBm)

If P1=P2, then Pin=P1+3dB or P2+3dB(dBm), and

IM3＝P1-P12＝P2-P21＝P2-P12＝P1-P21(dB)

For cascaded IIP3 using multiple nonlinear components, the formula is as follows:

where Gain = gain to component input.

Therefore, one way to improve the IIP3 of a receiver cascade is to reduce the gain before the first nonlinear component. In this case, the LNA and mixer limit the IIP3. However, another quantity needs to be defined to set the sensitivity or minimum received signal level without interference. This quantity is known in the art as Noise Figure (NF). If the gain of the receiver is reduced to improve IIP3 (and noise immunity), NF (and sensitivity to small desired signals) is reduced.

Define the NF of a component as follows:

NF=Si/Ni-So/No(dB) of the component,

Where: Si/Ni is the ratio of input signal to noise expressed in dB,

So/No is the ratio of output signal to noise expressed in dB.

For components cascaded in the receiver, the formula is as follows:

where NFe is equal to the noise figure of the part,

NFi is equal to the cascaded noise figure to the part,

Gain is equal to the operational gain to the component.

An 'optimal' cascaded NF can be achieved if the gain of this component is maximized, which formula contradicts the requirement of an 'optimal' cascaded IIP3. For the specified one-by-one components, receiver NF and IIP3, there exists a finite set of gains for each component, satisfying all requirements.

Usually, the receiver is designed so that NF and IIP3 are predetermined constants, and these two quantities set the dynamic operating range of the receiver with and without interference. Optimize gain, NF and IIP3 for each device based on size, cost, heat, static and dynamic component current draw. In a dual-mode CDMA/FM portable cellular mobile communication receiver, the CDMA standard requires a 9dB NF at the minimum signal. In other words, for CDMA mode, the sensitivity requirement is an S/N ratio of 0dB at -104dBm. For FM mode, the requirement is an S/N ratio of 4dB at -116dBm. In both cases, the requirement can be transformed into a requirement for NF as follows:

NF＝S(dBm)-S/N(dB)-N _therm (dBm/Hz)-signal BW(dB/Hz),

Among them, S is the minimum signal power,

S/N is the minimum signal-to-noise ratio,

N _therm is the lowest value of thermal noise (-174dBm/Hz@290K),

Signal BW (dB/Hz) is the bandwidth of the signal.

Therefore, NF of CDMA=-104dBm-0dB-(-174dBm/Hz)-61dB/Hz=9dB,

NF of FM=-116dBm-4dB-(-174dBm/Hz)-45dB/Hz=9dB,

Where -61dBm/Hz is the noise bandwidth of the CDMA channel,

-45dBm/Hz is the noise bandwidth of the FM channel.

However, the NF of the receiver is only required when the signal receives a minimum level, and the IIP3 is only required when there is interference or a strong CDMA signal.

There are only two ways to cover areas where carriers are generating high levels of interference. One is to use the same technology, even if the cell location is the same as the competitor's. The other is to improve the noise immunity of the receiver. One way to improve noise immunity is to increase the receiver current. However, this is not a practical solution since the portable radio receiver runs on batteries. Increasing the current drains the battery faster, thereby reducing the talk and standby time of the radiotelephone. There is therefore a need to minimize multi-tone interference in radiotelephones without compromising power consumption.

Contents of the invention

The present invention provides an apparatus for improving radio frequency interference immunity of a radio receiver, comprising: a first switch coupled to a received signal, the switch having a first position and a second position, the second position being coupled to a bypass path; A first amplifier for amplifying a received signal having an input connected to the first position of the first switch and an output connected to the bypass path; a controller connected to the first switch responsive to the received signal Exceeding a predetermined power level, the switch is switched to the closed position.

The method of the present invention comprises the steps of: detecting the power level of the received radio signal; and reducing the gain of the receiving amplifier if the power level is equal to or greater than a predetermined threshold.

Figure overview

Fig. 1 shows a block diagram of the device for improving the noise immunity of the receiver according to the present invention.

Fig. 2 shows a block diagram of another embodiment of the present invention.

Fig. 3 shows a block diagram of another embodiment of the present invention.

Fig. 4 shows a block diagram of another embodiment of the present invention.

FIG. 5 shows another graph of received RF input power versus carrier-to-noise ratio according to the embodiment of FIG. 7 .

FIG. 6 shows a graph of received RF input power versus carrier-to-noise ratio according to the embodiment of FIG. 8 .

Fig. 7 shows a block diagram of another embodiment of the present invention.

Figure 8 shows a graph of interference power versus signal power without the arrangement of the invention.

Fig. 9 shows a graph of interference power versus signal power according to another embodiment of the device of the present invention.

Fig. 10 shows a block diagram of another embodiment of the present invention.

Fig. 11 shows a block diagram of another embodiment of the present invention.

Fig. 12 shows a block diagram of another embodiment of the present invention.

Figure 13 shows a graph of nonlinear transfer characteristics versus distortion measurements.

Figure 14 shows the spectral description of the distortion components.

FIG. 15 shows a block diagram of a method for detecting received signal power according to the present invention.

Fig. 16 shows a flowchart of the fading control method of the present invention.

Embodiments of the present invention

The purpose of the present invention is to change the NF and IIP3 of the receiver to improve the IIP3 (or immunity) if necessary without affecting the NF. This 'boost' of performance is achieved by varying the gain of the first dynamic component in the receiver. It can be changed by changing the gain of the LNA in a continuous range or disconnecting the LNA with a bypass switch.

Figure 1 shows a block diagram of a preferred embodiment of the present invention.

This embodiment involves the use of an adjustable gain control (AGC) 110 to continuously adjust the LNA 115 at the front end of the receiver. A serial AGC110 on the front end also offers the benefit of being linear over a minimum RF input level, while an AGC120 on the transmit side may reduce the IF AGC125 and 130 requirements.

This embodiment detects the power output of the LNA 115 . The power detector 105 measures signal power and interference power at RF. Using this embodiment, the power detector 105 can continuously reduce the gain of the LNA 115 when the received power is lower than -65dBm in the embodiments of "Conversion Gain" in Figs. 7, 10, 11 and 12 described later.

In the preferred embodiment, the power detector 105 detects received signal and interference power at RF. This detected power is passed through the loop filter and used to adjust the receive AGC 110, thereby adjusting the intercept point of the receive elements. Decrease the gain when the measured power increases and increase the gain when the measured power decreases. In this embodiment, LNA115 and AGC110 can also be combined to form a variable-gain LNA, so a separate AGC110 block is not required. The power of the transmit AGC 120 placed before the power amplifier 150 is adjusted in the same way as the receive AGC 110 to maintain the overall transmit power level.

AGC amplifiers 125 and 130 are also provided after the mixers 135 and 140 to adjust the gain after the bandpass filter 145 filters out the interference. These AGC amplifiers 125 and 130 implement the normal CDMA functions of open loop power control, closed loop power control and compensation. These IFAGC125 and 130 are required due to the wide dynamic range of CDMA. Typically, these AGC125 and 130 have a gain range greater than 80dB. The receive and transmit AGCs 125 and 130 after the mixers are conditioned by another power detector which measures the total power of the down-converted received signal. Power detector 150 adjusts the gains of AGCs 125 and 130 downward when the power of the downconverted signal increases, and adjusts the gains of AGCs 125 and 130 upward when the power of the downconverted signal decreases.

In a preferred embodiment, the received signal is in the frequency band 869-894 MHz. The transmitted signal is in the frequency band of 824-849MHz. Another embodiment uses a different frequency.

The graph shown in Figure 5 illustrates the benefits of this AGC method. The left-hand y-axis shows the carrier-to-noise ratio versus received input power parameterized with respect to the interference level. The y-axis on the right-hand side shows the total interference power required for the constant C/J as a function of received input power. When interference is absent (-100dBm), the radio operates as if without RF AGC. When the interference increases, C/N decreases, but the effective linearity also increases. In this example, the RF dynamic range is 30dB, and the threshold where RFAGC works is located at the point where the interference power is greater than -25dBm.

Figure 2 shows another embodiment of continuous gain adjustment. This embodiment first filters out interference with the bandpass filter 205 before the power detector 210 determines the power level of the downconverted signal. Threshold detector 225 determines when the signal power level reaches a certain point (-105dBm in this embodiment), and then adjusts the gains of AGCs 230 and 235 downward when the signal power exceeds that power level. When the signal power level is below this threshold, the gains of AGCs 230 and 235 are adjusted upward. The gains of AGCs 215 and 220 before and after mixers 240 and 245 are continuously adjusted without checking a predetermined threshold of power, normal CDMA AGC power control.

Figure 6 shows a graph of this embodiment. When setting the threshold at -105dBm (minimum received RF level), C/N does not increase as rapidly as without RF AGC. The advantage of this embodiment is that there is a linear benefit at very low RF input power, no receive RF power detector is required, and the AGC loop only detects signal power. Therefore, the design of the AGC loop is simpler than that of detecting RF power.

Figure 3 shows another embodiment of the invention. The operation of this embodiment is similar to the embodiment of FIG. 1 . The only difference is to place the AGC301 before the LNA305 in the receive path.

Figure 4 shows another embodiment of the invention. This embodiment uses attenuator 405 between antenna 410 and duplexer 415 . The attenuator is controlled by a power detector 420 after the LNA 425 . Power detector 420 measures the received signal and interference power, filters it, and compares it to predetermined thresholds. In this embodiment, the threshold is -25dB. When the combined signal and interference power reaches the threshold, the attenuation of the attenuator 405 is increased. This adjustment can be performed in digital fixed steps or in a continuous manner. AGCs 430 and 435 after mixers 440 and 445 are adjusted in the same manner as the preferred embodiment of FIG. 1 .

Figure 7 shows another embodiment of the device of the present invention. This embodiment uses switches 701 and 702 to change the front-end gain. For a particular CDMA radiotelephone design, the actual switching level is related to the signal-to-noise ratio requirement as a function of signal level or noise figure. The present invention can be used with AMPS radiotelephones, however the switching characteristics will be changed to accommodate different operating points.

This embodiment includes an antenna 725 for receiving and transmitting signals. The receive and transmit paths within the radio are coupled to antenna 725 through a duplexer 720, which separates received signals from transmitted signals.

The received signal is input to LNA703, which is connected between two switches 701 and 702. One switch 701 couples the LNA 703 to a duplexer 720 and a second switch 702 couples the LNA 703 to a bandpass filter 704 . In a preferred embodiment, switches 701 and 702 are SPDT GaAs switches.

The LNA 703 is connected to one contact of each switch, and when the two switches 701 and 702 are switched to these contacts, the received signal is connected to the LNA 703 and the amplified signal of the LNA 703 is output to the band-pass filter 704 . In this embodiment, the frequency band of the bandpass filter 704 is 869-894MHz. Another embodiment uses a different frequency band depending on the received signal frequency.

Bandpass path 730 is coupled to the other contact of each switch. When switches 701 and 702 are switched to their other junctions, the received signal of duplexer 720 bypasses LNA 703 and is directed to bandpass filter 704 . These switches 701 and 702 are controlled by the radiotelephone microcontroller 740 in this embodiment. In another embodiment, separate controllers are used to control the positions of these switches.

After bandpass filter 704 filters the received signal, the filtered signal is downconverted to a lower intermediate frequency (IF) for use by the rest of the radio transceiver. Down-conversion is accomplished by mixing the received signal with another signal having a frequency set by the phase-locked loop 707 driving the voltage-controlled oscillator 706 by the mixer 705 . The latter signal is amplified by amplifier 750 before being input to mixer 705 .

The down-converted signal of the mixer 705 is input to the back-end AGCs 708 and 709 . These AGCs 708 and 709 are used by radiotelephones for closed loop power control, which is well known in the art.

In the method of the present invention, microcontroller 740 monitors the power of the received signal. When the power exceeds -65dBm, microcontroller 740 commands switches 701 and 702 to switch to the bypass position, thus coupling the received signal directly to bandpass filter 704. By bypassing the gain of the LNA 703, the intercept point of the receiver is increased in proportion to the reduction in gain in dB. Another embodiment uses other circuits and methods to monitor the power of the received signal.

Another embodiment of the inventive method continuously adjusts the gain of the front end. This embodiment uses a low power threshold such as -25dBm.

The graphs of FIGS. 8 and 9 illustrate the advantages of the switchable gain embodiments of the present invention shown in FIGS. 7 , 10 , 11 and 12 . Figure 8 shows a graph of interference power versus radio frequency (RF) signal power for a typical radio that does not use a switchable gain device. The curve shows that the maximum interference level is limited to the receiver input compression point of -10.5dBm. The figure shows the power curves for one and two tone signals.

FIG. 9 is a graph showing the variation of interference power received by a radio versus RF signal power received by a radio using the switchable gain method and apparatus of the present invention. It can be seen that at the -65dBm point of the curve, the switch is switched to bypass the LNA gain, so a large interference power can be tolerated without affecting the RF signal power. The figure shows the power curves for one and two tone signals.

Figure 10 shows another embodiment of the device of the present invention. This embodiment uses a SPST switch 1001 . In this embodiment, the controller 1020 switches the switch 1001 to the bypass path 1010 when the received signal power reaches -65 dBm. This effectively short-circuits the LNA 1002 gain, thus coupling the received signal directly to the bandpass filter 1003.

Figure 11 shows another embodiment of the device of the present invention. This embodiment uses a SPST switch 1105 which, when closed, shorts the LNA 1110 to ground through resistor 1101. This creates an impedance mismatch at the input, causing signal attenuation and, therefore, reducing the gain of the LNA1110. Same as the above embodiment, when the input signal power reaches -65dBm, the switch 1105 is closed. The resistance of resistor 1101 is related to the amount of attenuation required. In another embodiment, the resistance is different for different LNAs.

Figure 12 shows yet another embodiment of the device of the present invention. This embodiment uses a SPDT switch 1201 at the output of the LNA 1205. LNA 1205 is connected to one contact of switch 1201, and bypass path 1210 is connected to the other contact. The input of bypass path 1210 is connected to the input of LNA 1205 . When the power level of the received RF signal reaches -65 dBm, switch 1201 is thrown to bypass path 1210 from where it connects LNA 1205 to bandpass filter 1220 . This couples the signal directly to the bandpass filter 1220, bypassing the gain of the LNA 1205.

In all of the above embodiments, the power supply to the LNA can be turned off while being bypassed by the switch. This is accomplished by connecting the power supply terminals of the LNA to a switch that is also controlled by the controller. Once the LNA is bypassed and is no longer in use, turn off the power. This reduces the power consumption of the radio, thereby increasing the talk and standby time that the battery can use.

In another embodiment of the present invention, Ec/Io detection is used to determine when to adjust the front-end gain. Alternative embodiments use other mass scales, such as Eb/Io.

These ratios are quality measures of the performance of digital communication systems. The Eb/Io ratio represents the energy per bit versus the total interference spectral density of the channel, while the Ec/Io ratio represents the energy per CDMA chip (chip) versus the total interference spectral density. It can be considered that Eb/Io is a measure that expresses the characteristics of one communication system to another system; the smaller the required Eb/Io, the more effective the system modulation and detection process is for a given error probability. Assuming easy access to Ic/Io and received signal strength, when Ec/Io drops, the microcontroller can detect the presence of strong interference, while the AGC detector increases the interference. The microcontroller can reduce the front-end gain to improve noise immunity, which will improve Ec/Io and reduce interference components falling into the signal bandwidth.

When the signal quality reaches the above Eb/Io or Ec/Io thresholds, reduce the front-end gain. This gain adjustment can be accomplished using a continuous adjustment method or an amplifier switching method, or both.

Yet another embodiment shown in FIG. 15 would detect signal power at IF or baseband, rather than a combination of signal and interference power at RF. This method is relatively simple, it only has a power detector AGC control loop.

Figure 15 shows a block diagram of another method of detecting the power of a received signal. First 1501 downconverts the signal to baseband frequency. The analog signal is then converted 1505 to a digital signal for further baseband processing, which includes determining the strength of the received signal. Chip correlator 1510 determines the energy per chip for all non-correlated component energies. Processor 1515 uses this information along with a Received Signal Strength Indicator (RSSI) to determine the amount of gain adjustment for receiver 1520 and transmitter 1530 .

Since the received signal power scale includes both signal and interference power, receive gain increases only when both signal level and energy per chip decrease. Since the RSSI is changing, the transmit power must also be changed to compensate for the open loop power control to work properly. Thus, the processor adjusts the transmit gain whenever the receive gain is adjusted.

Other embodiments use clearing or signal power to control the variable gain AGC. Alternative embodiments only control receive power rather than both transmit and receive power.

FIG. 16 shows the gain control method of the above-mentioned embodiment. This method is based on the relationship shown in the graph of FIG. 13 . In Figure 13, it can be seen that as the interfering input power increases along the X-axis, the intermodulation products (lower curve) increase faster than the interfering power. Therefore, if interference occurs at the receiver input, applying XdB attenuation on the input will reduce the IM3 intermodulation product by 3 ^* XdB.

Typically, intermodulation products do not fall into the IF section of the radio due to their lower power. Intermodulation products outside the IF section do not cause receiver performance problems. Therefore, the gain of the receiver must only be adjusted if the intermodulation products have sufficient power to affect the IF signal.

Referring to FIG. 16, the method of the present invention first adjusts the input gain (1601). In a preferred embodiment, the gain adjustment is 3dB. However, other embodiments may use other gain adjustment values, such as a 1dB-6dB range. The receiver's processing is then used to measure the power variation of the received signal (1605). In the preferred embodiment, the automatic gain control process detects IF signal power changes. It should be understood that measuring the variation of the received signal can also be done at the RF level or at the baseband level of the receiver.

If the signal power varies by close to 3dB, the CDMA signal is above the noise floor and there is no potential for problematic intermodulation products. In this case, no additional gain adjustment is required, but increasing the gain will improve receiver sensitivity. The IF signal power variation close to (3+-0.5)dB is still regarded as 3dB.

If the IF signal power changes by less than 3dB (1610), the CDMA signal is below the noise floor, or there are no intermodulation products that could cause problems. In this case, the AGC sees only small CDMA signals and noise. Therefore, the gain (1615) of the receiving circuit must be increased to increase the sensitivity of the receiver.

If the IF signal power varies by more than 3dB, the intermodulation products are sufficient to cause problems and an additional gain adjustment 1620 must be made. In a preferred embodiment, if the input gain changes by 3dB, the intermodulation product will change by 9dB when a large interference occurs. In this case, the average gain can be reduced by a small amount (eg, 3dB) until the method of the present invention determines that the intermodulation products are reduced to an acceptable level.

The method of the present invention can be used to continuously check for intermodulation products at a low rate. In the preferred embodiment, this rate is 10 times per second. Other embodiments use the once-per-frame-period approach. Still other embodiments use other rates, such as checking only when larger errors are detected on the forward link.

In summary, the method of the present invention enables a mobile radio to travel close to antennas of a different system, while providing the radio immunity to radio frequency interference from another system. By reducing the front-end gain, the intercept point of the radio receiving circuit is increased so that distortion components caused by signals from other systems do not degrade receiver and demodulator performance.

Claims (10)

1, a kind of device that improves radio receiver radio frequency interference immunity to interference, this receiver is characterized in that in received signal described device comprises:

Be connected to first switch of the signal that receives, this switch has primary importance and the second place second place is connected on the bypass path;

First amplifier is used to amplify the signal that receives, and its input is connected on the primary importance of first switch, and output is connected on the bypass path;

Be connected to the controller of first switch, surpass predetermined power level in response to the signal that receives, switch transition on make position.

2, the device of raising radio receiver radio frequency interference immunity to interference as claimed in claim 1 is characterized in that, also comprises: second switch, have the primary importance and the second place, and primary importance is connected to first amplifier, and the second place is connected to bypass path;

Described controller also is connected on the second switch, and controller surpasses predetermined power level in response to the signal that receives, and first switch and second switch are transformed on the second place.

3, the device of raising radio receiver radio frequency interference immunity to interference as claimed in claim 1 is characterized in that predetermined power level is-65dBm.

4, the device of raising radio receiver radio frequency interference immunity to interference as claimed in claim 1 is characterized in that, amplifier is a low noise amplifier.

5, the device of raising radio receiver radio frequency interference immunity to interference as claimed in claim 1 is characterized in that, also comprises:

Be connected to the filter on first amplifier out, output is through the received signal of filtering on the filter output of filter;

Oscillator is used to produce the oscillator signal of preset frequency;

Have the frequency mixer of the first input end and second input, first input end is connected to the output of filter, and second input is connected to oscillator, and mixer response produces down-conversion signal in oscillator signal with through the received signal of filtering;

Second amplifier that connects down-conversion signal;

The 3rd amplifier that connects down-conversion signal;

Be connected to the first surface acoustic wave filter on second amplifier, be used to produce the signal that uses in the digital telephone system.

6, the device of raising radio receiver radio frequency interference immunity to interference as claimed in claim 1 is characterized in that described device also comprises:

Resistance, first end of resistance is connected to the primary importance of first switch, and second end of resistance is connected on the earthing potential.

7, a kind of device that improves radio receiver radio frequency interference immunity to interference, this receiver has received signal, it is characterized in that, and described device comprises:

Amplifier, the signal that its input receives is used for producing the received signal of amplifying at output;

Be connected to the bypass path of amplifier in;

Switch with primary importance and second place, primary importance are connected to the output of amplifier, and the second place is connected on the bypass path;

Be connected to the controller on the switch, surpass predetermined power level in response to the signal that receives, switch transition on the second place.

8, a kind of method that improves radio receiver radio frequency interference immunity to interference, radio receiver has reception amplifier and receives the electric wire signal of telecommunication, it is characterized in that, and described method comprises the following step:

The power level of the radio signal that detection receives;

If power level is equal to or greater than predetermined threshold, just reduce the gain of reception amplifier.

9, method as claimed in claim 8 is characterized in that, the step that reduces the reception amplifier gain comprises the bypass reception amplifier.

10, method as claimed in claim 8 is characterized in that, the step that reduces reception amplifier gain is included between the radio signal that receives and the reception amplifier and produces impedance mismatching.

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